The present invention generally relates to an inter-axle differential lock actuation sensing method and, more particularly, to an inter-axle differential lock actuation sensing method for a vehicle having a tandem drive axle assembly.
Tandem drive axle assemblies having a forward rear axle and a rearward rear axle in proximity with each other are well known. Such tandem drive assemblies are widely used on heavy duty trucks and other over-the-road vehicles, such as busses, which have a high vehicle weight and/or a high load carrying capacity. In such assemblies, both rear axles may be power driven.
An inter-axle differential (IAD) is commonly employed in such vehicles to split the input shaft torque between the front and rear axle of the tandem. It is common for a vehicle operator to engage and disengage a lock out that overrides or disables the IAD through the use of a pneumatic switch, which typically is mounted on the vehicle dash. The pneumatic switch, in turn, applies air to an axle mounted actuator, which engages a sliding dog clutch to “lock” the inter-axle differential.
However, there are several shortcomings to the above-described manual methods of engaging/disengaging the IAD. First, failure of the vehicle operator to notice wheel end slip occurring and engage the IAD, can result in spin out failures. Second, engagement of the IAD, while significant slipping is in process, can result in damage to the-drive axle. Third, leaving the IAD engaged for an extended length of time can result in “drive line wind-up” and a resulting inability to disengage the IAD without reversing the vehicle. As a result of these shortcomings, extended wear can occur and the operator may not notice the wear, as actual engagement and disengagement of the IAD is not typically indicated.
More recently, automatic inter-axle differential lockout mechanisms have come into use, where speed sensors have been employed to monitor wheel end speed. For example, U.S. Pat. No. 4,050,534 to Nelson et al. generally discloses means for sensing a difference in the rotational speeds of first and second rear drive axles, and means for actuating a lockup means in response to the rotational speed difference for a tandem axle drive.
U.S. Pat. No. 5,676,219 to Fruhwirth et al. teaches a system for controlling the axle differential locks for automotive vehicles. The axle differential locks appear to be controlled by wheel speed sensors that estimate inter-axle and cross axle slippage by comparing the rotational speeds of the wheels.
U.S. Pat. No. 5,927,422 to Schakel provides a method and apparatus for correcting drive wheel slip while utilizing wheel speed sensors to determine rotational speeds of the driveshaft and non-driven wheel. A central processor appears to compare the ratios of driveshaft speed to the non-driven wheel speed for locking various interaxle differentials.
U.S. Pat. No. 6,174,255 to Porter et al. discloses a differential lock control system that employs speed sensors and an articulation angle sensor that communicate speed signals and an articulation angle signal to a microprocessor for controlling the locks on front and rear differentials for an articulated work vehicle. It appears that in an automatic mode, the microprocessor controls the locking of the differentials by comparing predicted axle speeds to actual speeds received from the speed sensors and an articulation angle from the articulation sensor.
U.S. Pat. No. 6,336,069 to Hasegawa et al. teaches a front and rear wheel load distribution control system for an inter-axle differential. Means for measuring and eliminating rotational differentials between the axles that are used for operating an inter-axle differential lock are also taught. This appears to be achieved through the use of a crossing angle detection sensor in conjunction with front and rear axle rotations sensors.
U.S. Pat. No. 6,524,207 to Murakami et al. discloses a control method for an inter-axle differential system and at least three rotational frequency detectors are used to detect skidding and the like. A controller appears to detect at least any one of the three rotational frequencies and a rate of change with time of that particular detected rotational frequency and then the controller outputs a locking signal to an inter-axel differential lock.
However, even with current sensing means for controlling the engaging and disengaging of the inter-axle differential, improvements in the sensing means may still be sought, for example, providing fewer sensors, more accuracy, and less weight to the sensing required for inter-axle differential lock actuation.